The present invention relates to an electric power steering (EPS) apparatus equipped with a booster that outputs an output voltage obtained by boosting a power supply voltage, and to a booster.
In recent years, EPS apparatuses, which use a motor as a driving source, are widely used as vehicle power steering apparatuses. Some of EPS apparatuses include a booster circuit to boost a supply source voltage. Such an EPS apparatus controls a motor based on a boosted voltage, such that assisting force increases and the rise characteristic of the assisting force is improved.
For example, the EPS apparatus disclosed in Japanese Laid-Open Patent Publication No. 2003-319700 includes a booster circuit provided between a vehicle power supply and a drive circuit. The booster circuit includes a booster coil, a first switching element, and a second switching element. The power supply voltage is applied to one end of the booster coil. The first switching element selectively grounds the other end of the booster coil. The second switching element selectively connects and disconnects the node between the booster coil and the first switching element with an output terminal.
By turning on and off the first and second switching elements, the booster circuit boosts the power supply voltage and then smoothes the pulsating voltage and current with a smoothing capacitor connected to the output terminal. The booster circuit then applies the smoothed voltage and current to the drive circuit
When an assist control stops due to turning off of an ignition switch or an abnormality of the EPS apparatus, the output terminal of the booster circuit is disconnected from the motor, which is a load of the booster circuit. Therefore, if the boost control is stopped at the same time as the assist control is stopped, so that the smoothing capacitor is disconnected from the vehicle power supply, the energy stored in the smoothing capacitor is not consumed after the stop of the boost control, and the terminal voltage of the smoothing capacitor is maintained to a high level for an extended period of time. Such high voltage portions are limiting factors in maintenance. In this respect, the booster circuit of the publication has plenty of room for improvement.